1. Field of the Invention
This invention relates to the field of removing ash-forming, inorganic particles from carbonaceous particles. More precisely, this invention relates to processes for the separation of aqueous suspensions of agglomerated carbonaceous particles and associated inorganic material.
2. Description of the Prior Art
The method of separating carbonaceous particles from associated, ash-forming inorganic materials is known in the art. These procedures have been devised for treating mixtures which would otherwise be unsuitable for use. Dry and liquid combinations of carbonaceous particles and inorganic materials are produced by many standard mining procedures, and there is therefore readily available mixtures to which these processes are applicable.
The steps for causing the agglomeration of the carbonaceous particles are similar for many of the existing methods. A typical agglomeration procedure is disclosed in U.S. Pat. No. 3,856,668 issued to Shubert on Dec. 24, 1974. The disclosed procedure is used to clarify coal washery waste waters in a two-step process. The coal particles are first agglomerated by the intense mixing of a heavy hydrocarbon, preferably as a water emulsion, with the washery waste water. The mixture then contains water, inorganic particles, the heavy hydrocarbon and the agglomerated coal particles. These four constituents are generally found in all of the existing agglomeration techniques.
The carbonaceous particles are recovered from this mixture in a variety of ways. The separation techniques rely upon two properties of the agglomerated carbonaceous particles. First, the agglomerated particles form relatively large clumps or flocs which may be removed by passing the entire mixture through a fine screen. The agglomerated carbonaceous particles are retained as a cake on the screen and the water and suspended inorganic particles pass through. The second characteristic relied upon is the apparent specific gravity of the flocs. The flocs display an apparent specific gravity of less than 1, and therefore will float to the top of the water suspension. Conversely, the inorganic materials have a specific gravity of greater than 1 and will gradually settle to the bottom of the tank in which the water suspension is contained. Methods based upon these characteristics are disclosed in the Shubert patent previously cited. In U.S. Pat. No. 3,637,464, issued to Walsh et al. on Jan. 25, 1972, there is disclosed a similar agglomeration technique which utilizes a screen to separate the larger agglomerated particles from the water and the inorganic particles. Centrifuges have also been utilized for separating these materials as is disclosed in U.S. Pat. No. 2,769,537 issued to Reerink et al. on Nov. 6, 1956.